Focusing on solving the problem of high-precision machining of the lower end face of a sealed valve hole in an aviation valve body, we carried out independent research and adopted a face device motorized grinding end cap with adjustable/stabilized pressure, a pair of precision guides, spherical adjustment and transmission and positioning error compensation (ZL201820823098.4) The new processing technology has successfully solved the technical problems such as flatness, surface roughness and verticality according to the axis of the guide hole which require high precision at the lower end of deep holes, and extended the high precision processing technology to the lower end of the deep holes. It has the advantages of strong assembly practicability and high processing efficiency.
1 Preface
A certain servovalve product is designed with a special structure. A valve part is installed in a 94mm deep φ15H7 hole in the valve body part. The outer diameter of the valve and the inner diameter of the valve hole are connected by a sliding valve coupling joint (see the figure). 1). Realize oil circuit switching when the valve parts are in different positions due to force movement[1]. When normally closed, the lower plane of the valve hole also constitutes the sealing surface. Its flatness, surface roughness and perpendicular to the hole axis are as high as IT7 and above. Its bottom surface structure and characteristic values are shown in the figure. 2. shown.
a) The position of the valve connection holes B and C when opening
b) Position of valve connection holes A and B when normally closed
Figure 1 Schematic diagram of the drawer coupling joint
Figure 2 Schematic diagram of the lower end face of the valve hole and the structure of the valve hole
If this technical achievement is successfully implemented, a deep hole end underside grinding device with precision guidance, low pressing force and stable controllability should be developed based on the plane grinding principle to achieve precision machining of the lower hole end face. Due to the technical blockade imposed by foreign aviation technology on our country, it is difficult to obtain relevant grinding technology. In existing technology, magnetic abrasive magnetic grinding technology is generally used to grind the bottom plane of the hole.[2]has advantages in finishing processing of complex curved surfaces. The surface roughness value is reduced and the efficiency is high. However, the ability to change or improve geometric accuracy such as ground plane flatness is poor, so versatility is poor. . In the prior art, there is also a method of grinding the lower end plane of the hole using a grinding rod with an end plane. For example, patent document CN201361804Y describes a deep downhole grinding tool for a CNC boring and milling machine. However, this grinding component has not yet been used. Considering the requirements of perpendicular of the end surface to be ground and the axis of the reference hole, and during actual operation, when grinding the bottom end plane of holes with different hole depths, it is necessary remove the cotter pin then separate the grinding rod from the transmission rod. Replace the grinding rod with the corresponding length. At the same time, the processing of deep holes and slotted structures is tedious, less efficient in the manufacturing process itself, and inconvenient to install.[3]。
The grinding component (patent number ZL201820823098.4) independently developed by this technological achievement can not only take into account quality requirements such as flatness, surface roughness and circularity with respect to the hole axis of reference of the lower end surface of the hole, but also can be used for surface grinding of different hole depths, it can be stopped directly, and the corresponding grinding rod can be removed and replaced. The operation is more convenient and can further improve grinding efficiency.
All existing key technologies have been solved, and various technical indicators have not only met the design quality requirements, but also reached the national advanced level. This technological achievement has been successfully promoted and applied in the production of valve body parts for servovalve products supporting a variety of domestic key aircraft models, generating considerable economic benefits and contributing to the development of China’s aviation industry. my country.
2 Research Ideas
2.1 Analysis of process difficulties
For deep hole processing, flat bottom processing is a traditional processing difficulty. Especially for the valve hole of this project, the ratio of hole depth to hole diameter exceeds 6:1, which belongs to deep hole processing. Due to poor tool rigidity and strong tool vibration and deflection, it is difficult for traditional turning and boring methods to simultaneously ensure surface roughness, flatness and circularity compared to the reference hole at the bottom of high precision deep holes. The existing grinding and polishing technology cannot take into account the three key indicators of this project, so it is necessary to conduct technical research on hole bottom surface grinding.
In addition, the key features of this project, the flatness of the lower end face of the hole 0.01mm and the perpendicularity of the lower end face of the hole and the axis of the hole corresponding to the valve 0.03 mm, can be directly detected using three-dimensional coordinates, but the surface roughness value of the bottom side of the hole Ra = 0.1 μm, due to the fact that the hole is deep and the Surface roughness meter cannot perform direct detection, so a reliable indirect measurement method must be sought.
2.2 General idea
1) The φ15H7 hole is suitable for the micro clearance of the valve, making full use of precision coupling subprocessing technology to develop precision guide post and guide ring tooling to meet high verticality precision and other requirements. on existing technology, principles and experience of plane grinding to develop adjustable stabilizing pressure/force, and adopts ball joint connection and infinite error mechanism design[4]to carry out precision machining of the underside of the hole.
2) Grinding is a finishing process, suitable for processing with small tolerances of micro-machining, and the self-damage of grinding tools is serious. In order to improve production efficiency, it is necessary to develop a new bottom treatment process. hole before grinding.
3) Considering the difficult problem of measuring the surface roughness value Ra = 0.1 μm on the bottom surface of the hole, the first workpiece cutting inspection method is adopted to solve the problem.
Therefore, the key to the success of this project lies in the developed grinding tooling process equipment, which must simultaneously meet the requirements of surface roughness, flatness and verticality, and meet the efficiency requirements of on-site production.
2.3 Technical solutions
(1) Development of grinding device Taiwan independently develops a new type of motorized hole lower end surface grinding device to achieve high-quality and efficient grinding processing of the lower end surface of hole and meet the final product requirements, the more. the important thing is the surface grinding of the lower end of the hole. The grinding device should take into account the flatness and roughness of the surface of the underside of the hole, as well as the verticality requirements relative to the reference hole axis, and use high-precision corresponding holes as guides in order to guarantee. Faced with this quality requirement, the project team independently developed a grinding device (grinding component ZL201820823098.4).
Downhole plane grinding requires not only a lower surface roughness value, but above all a higher plane accuracy.[5]the lower the flatness error value, the better, and it is necessary to reduce the reliance on highly skilled operators during (traditional) grinding operations and reduce labor intensity, thereby improving the grinding efficiency.
(2) The structure of the grinding device. The designed and manufactured grinding device is a motorized hole bottom end surface grinding device (see Figure 3), which provides reliable power using stepless speed adjustment and height adjustment. ‘limited tool (such as contact details). boring machines and other equipment). The grinding device consists of 4 parts: a tension regulating/stabilizing mechanism, a ball head auxiliary transmission mechanism, a pair of guides and a grinding rod. Tension regulation/stabilization mechanism, controllable spring compression to stabilize the force on the grinding surface. The ball head auxiliary transmission mechanism facilitates clutch operation. The function of the ball head is to correct and compensate the verticality error between the end surface of the grinding rod and the spindle axis when installed, thereby ensuring that the end surface of work of the The grinding rod and the end surface to be ground are tightly fitted. That’s the key. The outer circumferential surface of the pin is designed to be lower than the center of the ball head. The guide pair is suitable for guiding when grinding the bottom of deep holes to ensure the circularity requirements between the end surface to be ground and the reference hole. When designing a shallow hole bottom end surface grinding device, there is no need to design a guide, and the spherical head can be automatically aligned directly so that the end surface of work of the grinding rod fits the end surface to be ground. The grinding rod itself requires high manufacturing precision. For example, the flatness of the grinding end face and the circularity of the grinding end face with respect to the rotation reference axis are necessary to achieve the vein size at the same time. The end face of the grinding rod affects the quality and efficiency of grinding. It’s also huge. The design experience of “well” grooves (groove width 0.25mm, depth 0.5~1mm, spacing 1mm, and evenly distributed) obtained by experimental verification has the effect of improving the quality and efficiency when grinding the underside of the φ15H7 hole with a depth of 94 mm Better (see Figure 4 and Figure 5).
Figure 3 Structure of grinding device
Figure 4 Veins on the end surface of the grinding rod
Figure 5 Comparison results of grinding effects
The production requirements for this device are also very high. During the construction of the process, the mating parts with a corresponding gap of 0.004-0.006mm need to be sharpened/ground to process the inner hole, and centerless grinding/cylindrical grinding to process the cylindrical precision clearance to meet the positioning and guidance functions. For joints with a corresponding gap of 0.03 mm, processing techniques such as boring/turning are adopted to meet the assembly requirements (see Figure 6).
Figure 6 Actual tooling
Practical steps for tooling are as follows.
1) Determine the degree of compression of the spring based on the elastic force of the spring (see Figure 7), draw a marking line on the outer surface of the guide rod (a red marker will be sufficient) and pre-tighten the cylinder to fix. he.
Figure 7 Spring Compression Amount
2) The machine tool chuck holds the tension regulating/stabilizing mechanism, as shown in Figure 8.
Figure 8 Tooling Test
3) Place the workpiece correctly or fix it with a support so that the surface to be ground is in a horizontal state.
4) Adjust the machine tool or parts so that the concave spherical surface of the guide rod fits the convex spherical surface of the grinding rod, and check whether the installation is in place by loosening the cylinder screw.
5) Apply a uniform thickness of abrasive paste to the grinding end surface of the grinding rod, place the grinding rod into the corresponding hole, and manually confirm that the installation is in place.
6) Insert the pin rod into the hole corresponding to the ball head of the grinding rod, so that the exposed lengths of the two ends of the pin rod are approximately equal, and manually confirm that the connection is reliable.
7) Set the machine tool parameters, start the machine tool for grinding operation and stop it after grinding for a single duration.
Enter the next operation cycle until the quality of ground end surface is qualified. It should be noted that when removing the grinding rod after each grinding cycle, water sandpaper should be used to clean the surrounding burrs.
This device meets the production needs of continuous and stable grinding operations. It not only makes the quality of the grinding surface meet the design quality requirements, but also improves the grinding efficiency by more than 5 times compared with traditional manual grinding. the operator skill level requirements are greatly reduced, and it is not necessary to designate installation technicians and personnel with higher skill levels to operate (you only need to be able to operate the equipment) greatly reduces the labor intensity of operators.
Figure 9 shows the grinding test and the empirical parameters were obtained through several tests. Experiment data for grinding surface 1 of φ15mm: spindle speed 60rpm, spring elastic force 4.6N·mm, W5 coating grinding paste film thickness about 0.2mm , grinding duration 15 s/time. Experiment data for grinding surface 2 of φ15mm: spindle speed 60rpm, spring elastic force 4.6N·mm, M5 grinding paste film thickness of about 0.4mm, duration grinding 2.5 s/time. It should be noted that regardless of the method used, there is a risk of grinding scratches if the waiting time is too long. The grinding paste should be replaced in time, and the cycle operation should be carried out until the parts are qualified.
a) Display of test specimens
b) Functional test
Figure 9 Grinding test
Using this tooling and the above-mentioned exploration parameters and equipment, process the sample parts first and the measurement data is qualified. After exploring the processing experiment, the parts are processed and cut. After the measurement data of the first part meets the quality requirements, it will be produced in batches. The actual operation process and test records are shown in Figures 10 to 12.
Figure 10 Grinding sample
Figure 11 Grinding Parts
Figure 12 Part measurement results
The results of testing and comparisons of the main technical indicators and product design indicators of the main parts of the project of this technical achievement are presented in Table 1.
Table 1 Comparison of main technical indicators and product design indicators of the main parts of the project
After testing, all technical indicators of this product meet the design requirements. After being installed on the product, it works reliably and provides stable performance.
3 Conclusion
This technology has successfully solved the process and technical problems such as flatness, surface roughness and verticality depending on the guide hole axis which require high precision at the lower end of deep holes. The production process is efficient and the quality is stable and consistent. , guaranteeing that it matches a certain domestic key aircraft model. Smooth delivery of servovalve products.
The grinding component of this technology has great versatility in its voltage stabilization/regulation device. It can not only adjust the grinding force, but also be adapted to the structure of the grinding rod or polishing rod connected by its spherical transmission/precision guide post; structure, it is highly usable in the design and manufacturing of fixing structures and has been extended to the structural design of motorized polishing devices. The overall structural design of this grinding component has outstanding advantages and has broad application prospects in hole lower end surface grinding and surface R-shaped convex sealing structure polishing operations. lower end of hole.
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